Circularly polarizing plates and elliptically polarizing plates are a combination of optical films, which have a suitable phase difference, on a polarizing plate, and they are used as one member of liquid crystal display devices for the reason that they are essential to the principle of operation of the display, and for the object of solving the problem of viewing characteristics. Since these various circumstances in terms of the visibility are different depending on the method, which is determined by the positional relationship between the light source and the liquid crystal, such as the LCD method (for example, a STN type LCD, a TFT-LCD, an IPS (In-Plane Switching) type LCD, a FLC (Ferroelectric Liquid Crystal) type LCD, an OCB (Optically Compensated Bend) type LCD, a VA (Vertically Aligned) type LCD, an ECB (Electrically Controlled Birefringence) type LCD, a HAN (Hybrid Aligned Nematic) type LCD, a GH (Guest-Host) type LCD, and the like), the transmission type, the reflection type, and the semi-transparent type, circularly polarizing plates and elliptically polarizing plates that are suitable for each method become necessary.
For example, in order to solve the problem in STN type liquid crystal display devices (LCD) wherein the screen becomes colored as a result of the phase difference applied at the time of passing through the crystal, and in order to solve the problem in a TFT-LCD wherein the display color and the display contrast changes depending on the viewing direction, a linearly polarizing plate and an elliptically polarizing plate, in which optical films have been combined, are utilized.
Furthermore, in reflection type, transflective type, and microreflection type LCDs, in which outside light is utilized as the light source, a circularly polarizing plate, in which a one-quarter wavelength plate has been combined with a linearly polarizing plate, is used.
Moreover, a normal one-quarter wavelength plate has a phase difference of one-quarter of a wavelength at only a single wavelength, and at other wavelengths the phase difference deviates from this value. Therefore with an object of making it function as a one-quarter wavelength plate over all of the visible region, wideband circularly polarizing plates wherein a wideband phase difference film, in which a single sheet or a plurality of sheets of one-half wavelength plates and one-quarter wavelength plates have been laminated, and a linearly polarizing plate, have been combined, and wideband elliptically polarizing plates wherein a phase difference film, in which a plurality of phase difference films have been laminated, is combined with the polarizing plate, are also being developed.
Normally, circularly polarizing plates, in which a polarizing plate and a one-quarter wavelength plate have been combined, are prepared by respectively laminating the polarizing plate and the one-quarter wavelength plate. At this time, they must be laminated such that the angle between the absorption axis of the polarizing plate and the slow axis of the one-quarter wavelength plate strictly meets 45°. Furthermore, in the same manner, in the wideband circularly polarizing plate, in which a polarizing plate and a wideband phase difference film, wherein a plurality of wavelength plates have been laminated, have been combined, there is a need to strictly control the lamination angle relating to the azimuth of each wavelength plate, and the lamination angle between the wavelength plate and the absorption axis of the polarizing plate.
Furthermore, in a case where it is used for a liquid crystal display element, the angle formed between the optical axis of the wavelength plate and the alignment direction of the liquid crystal must also be precisely made a designed value.
Conventionally, a birefringent aligned film is used for the phase difference film, although in recent years, as a phase difference film having more complex optical characteristics, optical films, where a polymerizable liquid crystal is applied on a substrate in which an alignment film has been provided, and cured in a state where the liquid crystal molecules are aligned, are being developed. Specifically, a film of a polymer, such as a polyimide, is provided on the substrate, the polymerizable liquid crystal is applied on an alignment film, in which the polyimide has been rubbed (rubbing method) in a single direction with a cloth, or the like, the liquid crystal molecules are aligned in the rubbing direction and the alignment is fixed by polymerization thereafter, and as a result of the combination between the alignment direction of the alignment film and the alignment form of the polymerizable liquid crystal, a phase difference film having optical characteristics that cannot be obtained in an aligned birefringent film, can be obtained.
However, in regard to the rubbing alignment film, there is a problem in that scratches and dust can occur at the time of the rubbing process. The generated dust can be removed by washing, or the like, but since scratches cannot be removed, there is concern that the optical uniformity of the laminated liquid crystal film will be greatly impaired. Furthermore, in a production process using a rubbing type alignment film and a roll form long length film, since there is a boundary in the rubbing direction with respect to the transportation direction of the film, it is in fact impossible to make the slow axis of the phase difference film the aforementioned lamination angle while it is a long length film. Therefore, in a normal production process, a method in which a rectangular shaped film is cut out of the long length film and laminated such that it becomes a suitable lamination angle, or a method in which films that has been cut out are laminated at a suitable angle, have been used. Accordingly, a very complex process had to be performed. Furthermore, since there was a need to incline the direction of cutting out with respect to the longitudinal direction of the long length film, there was a problem in that unusable portions, which were left behind after cutting, were generated. Furthermore, lamination accuracy could not be sufficiently obtained with respect to the desired lamination angle obtained from the aforementioned simulations, or the like, and there was a problem in that an optical film that has optical functions as designed could not be obtained.
Photoalignment films are known as an alignment film in which rubbing is not performed. The photoalignment method is one alignment method that is able to align the liquid crystal molecules without rubbing, and can generate a liquid crystal alignment capability in the film by simply irradiating light on a film that has been formed on the substrate and without making contact. The alignment can be controlled by the direction of the light, and in contrast to the rubbing method, since it has characteristics such as there being fundamentally no possibility of scratches and generated dust, there is a larger degree of freedom in the alignment state on preparing a phase difference film using a liquid crystal having a polymerizable group, there are no light leakages due to scratches, and a uniform film can be formed.
For example, a photoalignment film that is obtained by, applying a photoaligning polymerizable composition containing a dichromatic dye having two or more polymerizable groups in a single molecule on a substrate, and polymerization of the polymerizable groups by heating or irradiation of light following application of a photoalignment function by irradiating a polarized light (for example, refer to Patent Document 1), or a photoalignment film obtained by applying a polymerizable material, such as polyvinyl cinnamate, on a substrate, followed by a reaction performed by irradiating an anisotropic light (for example, refer to Patent Document 2), are known. Furthermore, an optical film comprising a photoalignment film comprising polyvinyl cinnamate as disclosed in Patent Document 2, and a polymerizable liquid crystal, is also known (for example, refer to Patent Documents 3 and 4). However, in regard to the optical films obtained using these photoalignment films, peeling, or the like, occurred at the interface between the photoalignment film and the polymerizable liquid crystal, and there was a problem in that the durability was inferior.
As an optical film with excellent durability, an optical compensation sheet with a superior durability, in which rubbing is performed on a polymer coating film, which has polymerizable groups, that is provided on a substrate, a discotheque liquid crystal that has polymerizable groups is applied thereon, and an optically anisotropic layer comprising the rubbing alignment film and the discotheque liquid crystal is chemically bonded via the interface, is known (for example, refer to Patent Document 5). However, since the method uses a rubbing alignment film, the problems that originate from the rubbing alignment film still cannot be solved. Furthermore, the optical compensation sheet relates to a perpendicular alignment film in which the in-plane direction of the discotheque liquid crystal molecules has been aligned in the perpendicular direction with respect to the substrate, and since the surface energy of the alignment film surface has been lowered by introducing long-chain alkyl chains or aliphatic chains, there was a tendency for the liquid crystal molecules to aggregate at the surface of the perpendicular alignment film, and there was a problem in that it was difficult to laminate in a thin-film state.
On the other hand, as a problem that is unique to laminated films, for example, there are cases where interface reflections occur at the boundary between the liquid crystal alignment film and the polymerizable liquid crystal layer, and there are cases where a problem occurs in that the desired transmitted light intensity is not obtained. This does not become so much of a problem in the case of an optical film comprising only an alignment film and a polymerizable liquid crystal layer (that is to say, there is one lamination interface), although in optical films where multiple layers have been laminated, such as wideband circularly polarizing plates in which a wideband phase difference film, comprising a single sheet or a plurality of sheets of one-half wavelength plates and one-quarter wavelength plates that have been laminated, and a linearly polarizing plate have been combined, or wideband elliptically polarizing plates wherein a phase difference film, in which a plurality of phase difference layers have been laminated, and a polarizing plate have been combined, since the number of lamination interfaces becomes numerous, it becomes a large cause for decreases in the transmitted light intensity. Consequently, the contrast demanded of the display decreases, and in particular, because the transmitted light intensity decreases in directions inclined from the screen normal, there were problems such as the deterioration of the viewing angle characteristics.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2002-250924    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. Hei 07-138308    Patent Document 3: Japanese Unexamined Patent Application, First Publication No. Hei 06-289374    Patent Document 4: Japanese Unexamined Patent Application, First Publication No. Hei 08-15681    Patent Document 5: Japanese Unexamined Patent Application, First Publication No. Hei 09-152509.